출처 : http://www.codeproject.com/cs/samples/linenumberingapp.asp

c#

public void ConvertText()
{
  StringBuilder output = new StringBuilder();

  try  {
	  char[] end_of_line = {(char)10};
	  string[] lines = this.Text.Split( end_of_line );

	  int line_count = lines.GetUpperBound(0)+1;
	  int linenumber_max_width = line_count.ToString().Length;

	  string padding = new String( ' ', this.LineNumberPaddingWidth);

	  for ( int i=0; i<line_count; i++ ) {
		  output.Append( this.GetFormattedLineNumber( i+1, linenumber_max_width, padding ) );
		  output.Append( lines[i] );

		  output.Append( "\r\n" );
	  }

	  if ( this.ConvertTabsToSpaces ) {
		  string spaces = new String( ' ', this.TabToSpacesWidth);
		  output = output.Replace( "\t",  spaces );
	  }

  } catch ( Exception e )  {
	  output.Append( e.Message );
  }

  this.Text = output.ToString();
}